1. Technical Field
The present invention relates to multi junction photovoltaic devices, and more particularly to textured multi-junction photovoltaic devices and fabrication methods that result in increased efficiency.
2. Description of the Related Art
Solar devices employ photovoltaic cells to generate current flow. Photons in sunlight hit a solar cell or panel and are absorbed by semiconducting materials, such as silicon. Carriers gain energy allowing them to flow through the material to produce electricity. Therefore, the solar cell converts the solar energy into a usable amount of electricity.
A photon need only have greater energy than that of a band gap to excite an electron from the valence band into the conduction band. Since solar radiation is composed of photons with energies greater than the band gap of silicon, the higher energy photons will be absorbed by the solar cell, with some of the energy (above the band gap) being turned into heat rather than into usable electrical energy.
To enhance efficiency of solar cells, multi-junction cells have been developed. Multi-junction cells include two or more cells stacked on top of each other. Any radiation transmitted through a top cell has a chance of being absorbed by a lower cell.
Multi junction solar cells composed of a stack of semiconductor materials with different band gaps offer higher cell efficiency, but further improvements in efficiency are desirable and needed.